1. Field of the Invention
The present invention relates to door alarms, and more particularly pertains to a new and improved alarm system which combines infrared and capacitive discharge sensors to provide discrete signals upon the approach of an individual and the touching of the door knob by the individual. Various types of infrared, photoelectric and mechanical alarm devices have been developed for the detection of the tampering of a lock mechanism by an individual. These conventional types of alarm systems do not provide separate indications depending whether an individual has merely approached the door or is actually tampering with the lock mechanism. The alarm system of the present invention is also useful as a door bell. Conventional alarm systems are complicated, expensive and difficult to install. The present invention overcomes these problems by providing an alarm system formed integrally with a door knob. Thus, the alarm system of the present invention may be installed by merely replacing the door knob.
2. Description of the Prior Art
Various types of door alarms are known in the prior art. A typical example of such a door alarm is to be found in U.S. Pat. No. 1,604,978, which issued to T. Cronin on Nov. 2, 1926. This patent discloses an alarm which is mechanically actuated by contacts in a door latch mechanism. U.S. Pat. No. 1,639,565, which issued to G. Jakopec et al on Aug. 16, 1927, discloses a door alarm device which activates an alarm upon operation of the sliding bolt of a door lock mechanism. U.S. Pat. No. 1,695,077, which issued to A. Zukor et al on Dec. 11, 1928, discloses a combined door latch and alarm. When forced entry is attempted, the door latch mechanism actuates a mechanical rotary bell. U.S. Pat. No. 3,659,549, which issued to W. Wagner on May 2, 1972, discloses a lock alarm mechanism for vending machines which utilizes a key operated latch member on a hinged housing door which actuates an alarm upon attempted forced entry of the door. U.S. Pat. No. 3,785,230, which issued to R. Lokey on Jan. 15, 1974, the disclosure of which is hereby incorporated by reference, discloses an automatic safety brake for a rotary saw which utilizes a capacitive discharge sensor which actuates an alarm bell upon approach of an individual's hand within close proximity to the saw blade. U.S. Pat. No. 4,453,390, which issued to P. Moritz et al on June 12, 1984, discloses a lock monitoring alarm. A photo sensitive circuit is utilized to detect and monitor the position of the lock. A visual display is provided for allowing individuals to monitor the condition of the lock from a remote location.
While the above mentioned devices are suited for their intended usage, none of these devices provide a door alarm system which activates separate discrete signals indicating the approach of an individual to a door and the touching of the door knob by the individual. Further, none of the aforesaid devices provide a combination infrared and capacitive discharge proximity sensor integrally formed with a door knob. Inasmuch as the art is relatively crowded with respect to these various types of door alarms, it can be appreciated that there is a continuing need for and interest in improvements to such door alarms, and in this respect, the present invention addresses this need and interest.